Diffuser

ABSTRACT

An improved diffuser apparatus for use in connection with gas turbines that will markedly increase the fuel efficiency of the turbine. The improved diffuser apparatus improves the performance of the diffuser apparatus by insuring that the gas flow supplied by the turbine is free from unnecessary energy losses due to improperly located mechanical structures. More particularly, the prior art turbine is modified in a manner to incorporate into the diffuser itself certain of the mechanical structures that previously formed a part of the structure of the turbine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to devices for the transformation of part of the kinetic energy of a moving fluid into pressure of the fluid. More particularly the invention concerns a diffuser for use in connection with gas turbines, where an improvement of performance is obtained at the interface between the turbine and the diffuser.

2. Discussion of the Prior Art

Novel and highly successful short subsonic diffusers are described in U.S. Pat. Nos. 3,599,431, 4,029,430 and 5,603,605, all issued to the present inventor. Because of the pertinence of these three patents, and because the present invention comprises an improvement over the inventions disclosed in these patents, U.S. Pat. Nos. 3,599,431, 4,029,430, and 5,603;605 are incorporated by reference as though fully set forth herein.

The diffusers described in detail in the incorporated by reference patents recover a major fraction of the kinetic energy in the stream of gas issuing from the last stage of the turbine and efficiently transform it into an increment of static pressure and, therefore, results in an improvement of the thermodynamic efficiency of the turbine. However, a part of the kinetic energy of the gas at the inlet of the diffuser is not available for recovery because the original design of the turbine did not contemplate the possibility of the level of energy recovery enabled by the advanced diffuser of the present invention; hence, attention to the interface between the turbine and the diffuser permits an additional pressure recovery increment if the diffuser corrects the defects in the flow of the gas from the last stage of the turbine.

Accordingly, the improved diffuser of the present invention is instantiated by transferring to the structure of the diffuser certain mechanical elements that are traditionally part of the turbine structure downstream of the last stage of the turbine. The removal of these mechanical elements from the turbine improves the gas flow to the diffuser and hence improves the energy recovery by the diffuser. As will be discussed in greater detail in the paragraphs that follow, the original function of these mechanical elements can be uniquely incorporated into the structure of the diffuser in such a way as to not affect the mechanical performance of the turbine, while at the same time relying upon the diffuser itself to provide the necessary structural support.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a diffuser apparatus for use in connection with gas turbines that will markedly increase the fuel efficiency of the turbine.

More particularly it is an object of the present invention to improve the performance of the diffuser apparatus by insuring that the gas flow supplied by the turbine is free from unnecessary energy losses due to improperly located mechanical structures.

Another object of the invention is to modify the prior art turbine in a manner to incorporate into the diffuser itself certain of the mechanical structures that previously formed a part of the structure of the turbine.

Another object of the invention is to modify the prior art turbine in the manner described in the preceding of paragraph without adversely affecting the aerodynamic function of the diffuser.

Another object of the invention is to identify the stress path in the structure of the diffuser to insure adequate rigidity against deformations previously resisted by the structural elements of the turbine that were removed from the turbine and incorporated into the diffuser itself.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side-elevational, cross-sectional view of one form of prior art diffuser structure that can be modified in accordance with the methods of the present invention.

FIG. 2 is a side elevational, cross-sectional view similar to FIG. 1, but showing the structural elements that formed a part of the prior art diffuser structure, but were, for sake of clarity, eliminated from FIG. 1 of the '605 patent.

FIG. 3 is a side-elevational, cross-sectional view of one form of the improved diffuser of the present invention.

FIG. 4, is a side-elevational, cross-sectional view of an alternate form of the improved diffuser of the invention.

DESCRIPTION OF THE INVENTION

Referring particularly to FIG. 1, one form of prior art apparatus that can be modified in accordance with the methods of the present invention is there shown. More particularly, FIG. 1 illustrates the apparatus shown and described in incorporated by reference U.S. Pat. No. 5,603,605 ('605) that comprises a diffuser coupled with a gas turbine of conventional construction. It is to be noted that the diffuser structure of this prior art apparatus is symmetrical about the axis 34 of the turbine. The turbine portion of the apparatus includes a power shaft 36 that comprises rotating hub 38 to which a plurality of outwardly extending turbine blades 39 are affixed. Circumscribing shaft 36 is a diffuser shroud 40 having inner and outer walls 42 and 44 respectively. As indicated in FIG. 1, the inner open mouth 46 of the shroud 40 is disposed proximate blades 39 of the turbine and functions to receive the high velocity gas stream generated by the turbine blades. Shroud 40 also includes an outer discharge area 48 which communicates with a novel collector means shown here as a collector structure 50. A capture means is disposed interiorly of collector structure 50 and functions to collect a portion of the gases flowing through the shroud. This capture means is here shown as a generally toroidal-shaped capture scoop 52 having an uninterrupted inlet 54. Inlet 54 is strategically located so that it directly faces the high velocity region of the gas stream flowing through shroud 40 toward discharge area 48. Inner wall 42 of shroud 40 is provided with a plurality of injection slots 56 while outer wall 44 is provided with a plurality of injection slots 58. A first plenum 60 circumscribes a portion of the inner wall 42 of shroud 40 and functions to feed gases into shroud 40 through injection slots 56. Similarly, a second plenum 62 circumscribes a portion of the outer wall 44 of shroud 40 and functions to feed gases into the shroud 40 via injection slots 58. As indicated in FIG. 1, each of the injection slots 56 and 58 are constructed so as to have a sharp trailing edge 56 a and 58 a respectively for introducing a thin sheet of fluid tangential to the respective inner and outer walls of the shroud and into the boundary layer fluid for the purpose of preventing the detachment of the gas stream from the wall.

Interconnecting first plenum 60 with toroidal structure 52 is at least a first tube or conduit 66. Interconnecting second plenum 62 with toroidal structure 52 is at least one second tube or conduit 68. With this novel construction conduit 66 supplies gases collected through opening 54 b of toroidal structure 52 to injection slots 56 while conduit 68 supplies gases collected through opening 54 c of the toroidal structure to injection slots 58. Exhaust gas from collector 50 is exhausted to atmosphere through an exhaust stack 70.

Turning to FIG. 2 of the drawings, this drawing shows the structural elements that formed a part of the prior art diffuser structure, but were, for sake of clarity, eliminated from FIG. 1 of the '605 patent. These important structural elements, which in the prior art apparatus functioned to maintain rigid concentricity, comprise a plurality of radial struts “RS” (typically five or six in number) that interconnect the outer wall of shroud 40 to a stationary hub generally identified as “SH” via an inner ring “IR”. Also forming a part of the prior art diffuser structure, but were, for sake of clarity, eliminated from FIG. 1 of the '605 patent is an outer ring “OR”.

As illustrated in FIG. 2, the radial struts “RS” are directly in the path of the gas flowing between the last turbine blade 39 and the first slots 56 and 58 of the diffuser and present an undesired obstruction to the free flow of the gas. More particularly, in the prior art construction illustrated in FIG. 2 of the drawings each radial strut “RS” creates a turbulent wake in which the stagnation pressure of the flow is reduced by a loss of momentum, thereby reducing the pressure recovery otherwise obtainable by the diffuser. In an attempt to reduce the swirl of the gas imparted to the radial struts by the last rotating blades, the radial struts in the prior art apparatus are sometimes configured to have an airfoil profile, similar to that of a stator blade. However, this approach works only at one point of RPM and load combination and for other RPM and load combinations the swirl is only partially removed generally at the cost of increased turbulence. In a conventional prior art diffuser the kinetic energy of the swirling gas is wasted and although the airfoil cross-section of the struts attempts to redirect at least part of the swirling gas in an axial direction, this approach succeeds only for a particular combination of load and RPM and, even in this case the wakes and turbulence limit the associated pressure recovery.

The diffuser illustrated and described in incorporated by reference Patent No. '605 re-directs the axial flow in a radial direction where any swirl present in the flow provides an added centrifugal pressure increment, regardless of the direction of the swirl. In this instance, there is no need to attempt to remove the swirl, since the diffuser itself converts the kinetic energy of the swirl into a greater pressure increment. However, as previously mentioned, the presence of the radial struts in the prior art apparatus, which are necessary for mechanical support, are detrimental to the pressure recovery by the diffuser.

The thrust of the present invention is to overcome this undesirable feature of the prior art apparatus and in so doing markedly improve the performance of the diffuser without adversely affecting the mechanical performance of the turbine. As will be discussed more fully in the paragraphs which follow, this is accomplished by modifying the prior art structure to, among other things, eliminate the struts “RS”.

Turning now to FIG. 3 of the drawings, one form of the improved apparatus of the present invention is there shown and generally designated by the numeral 100. This apparatus is similar in some respects to the prior art apparatus shown in FIG. 1 of the drawings and like numbers are used in FIGS. 1 and 2 to identify like components. As indicated in FIG. 3, the shaft that was designated in FIGS. 1 and 2 by the numeral 36 has been removed from the drawing, since the same diffuser structure is equally usable in connection with a turbine having a power takeoff shaft that protrudes from the opposite, or compressor end (see column 4, line 65 of the incorporated by reference '605 patent). Stationary hub “SH” houses bearings that are precisely concentric with the outer structures of the turbine and function to support the rotating parts of the turbine.

As is also shown in FIG. 3 of the drawings, the improved apparatus 100 here comprises combination conduit and structural support members 102 and 104 that take the place of the prior art conduits 66 and 68 and combination plenum and structural support members 106 and 108 that take the place of plenums 60 and 62. As indicated in FIG. 3, combination conduit and structural support member 102 and 104 function to provide rigidity to the diffuser, to maintain concentricity between hub “SH” and shrouds 40 and 42 during operation and to direct a portion of the high velocity gas stream captured by said capture means toward the injector slots provided in said inner wall of the shroud. Conduits 102 and 104, as well as plenums 106 and 108, have relatively thick sidewalls which, unlike the prior art conduits and plenums (which provided only gas pressure containment) function to provide substantial structural support to the diffuser. Accordingly, in the improved apparatus of the invention, the combination conduit and structural support members 102 and 104 and the combination plenum and structural support members 106 and 108 comprise load bearing structures as well as comprising structures for conveying gas from capture scoop 52 to slots 56 and 58.

Also forming a part of the improved apparatus 100 are substantially larger structural rings 110 and 112 that take the place of the prior art rings “IR” and “OR”. As shown in FIG. 3 of the drawings, structural rings 110 and 112 circumscribe and are connected to stationary hub “SH”. Additionally, the wall thickness of the generally toroidal-shaped capture scoop 52, which is designated in FIG. 3 by the numeral 114 has been substantially increased. With the construction thus described, combination plenum and structural support member 106 carries the stress from combination conduit and structural support member 102 to structural ring 110 which distributes the stress to the area of shroud 40 where former struts “RS” were previously anchored. Similarly, combination plenum and structural support member 108 carries the stress from combination conduit and structural support member 104 to structural ring 112, which distributes the stress to, and supports stationary hub “SH” as was previously done by struts “RS”.

The details of the design of load-bearing structures, such as combination conduit and structural support members 102 and 104 and combination plenum and structural support members 106 and 108, are well known in the art of mechanical design and involve careful consideration of the moment of inertia of the cross-sections, the modulus of elasticity of the material, and the overall curvature of the structures. In addition, the designer must take into consideration the differential thermal expansion coefficients required by the different temperatures of the gas flowing within the structure. No further discussion of the structural design is here required beyond emphasizing that the reinforced portion of the diffuser structure, including novel members 102, 104, 106 and 108, must be designed to maintain the required concentricity between stationary hub “SH” and shroud 40 under all operating conditions.

Alternate approaches to improving the performance of the diffuser without adversely effecting the mechanical performance of the turbine comprise adding the reinforcing structure directly to conduits 66 and 68 as described in connection with the embodiment of FIG. 3 and partially separating the load-carrying structure from the gas conveying structures in order to derive the maximum advantage from the geometry of the combined elements. One such approach is shown in FIG. 4, which comprises a partial external view of the reinforcing structure superimposed on the cross-sectional view of the improved diffuser, noting that the re-enforcements are mounted externally to collector structure 50 and join reinforced members 102 and 104 as shown.

In this case a first generally vertically extending reinforcement plate or built-up structural member 116, that is located in the vertical plane of symmetry of the diffuser can be connected to reinforced member 102 and extended to a ground-engaging plate 118 and can be used to support the weight of the diffuser as well as the weight of the exit section of the turbine. In this alternate embodiment, other reinforcements can be placed to the side to insure rigidity in the transverse plane. For example, a second reinforcement plate or built-up structure 120, which is operably associated with first generally vertically extending reinforcement plate 118, can be connected to reinforced member 102 in the manner shown in FIG. 4 of the drawings.

A mandatory requirement is that the rigidity combined with the mass of the supported elements results in a resonant frequency far from the operating RPM and its harmonics. This requirement dictates the number of reinforcing structures 120 and their location around the diffuser, with suitable spacing between them to accommodate the passage of exhaust stack 70.

Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims. 

1. A diffuser apparatus for use in connection with a gas turbine of the character having a rotatable power shaft and a plurality of rotating turbine blades, a high velocity gas stream exiting the turbine blades, said apparatus comprising: (a) a central hub for supporting said rotatable power shaft of said turbine; (b) a shroud circumscribing said hub, said shroud having inner and outer walls defining an enclosure having a first open end disposed proximate the turbine blades to receive the high velocity gas stream, and a second discharge end for exhausting gases of said high velocity gas stream, said inner wall of said shroud having first injector slots provided therein and said outer wall of said shroud having second injector slots provided therein; (c) capture means disposed proximate said second discharge end of said enclosure for capturing a portion of the gases of said high velocity gas stream; (d) first combination conduit and structural support member for providing rigidity to the diffuser and for directing a portion of the high velocity gas stream captured by said capture means toward said first injector slots provided in said inner wall of said shroud; and (e) a second combination conduit and structural support member for providing rigidity to the diffuser and for directing a portion of the high velocity gas stream captured by said capture means toward said second injector slots provided in said outer wall of said shroud.
 2. The diffuser apparatus as defined in claim 1 in which said capture means comprises a generally toroidal-shaped capture scoop.
 3. The diffuser apparatus as defined in claim 2 further including collector means circumscribing said discharge end of said shroud for collecting gases flowing therefrom, said generally toroidal-shaped scoop being disposed interiorly of said collector means.
 4. The diffuser apparatus as defined in claim 3 in which said collector means further includes: (a) a first combination plenum and structural support member circumscribing at least a portion of said inner wall of said shroud for providing rigidity to the diffuser, said first combination plenum and structural support member having a gas inlet and a gas outlet communicating with said first injector slots; and (b) a second combination plenum and structural support member circumscribing at least a portion of said outer wall of said shroud for providing rigidity to the diffuser, said second combination plenum and structural support member having a gas inlet and a gas outlet communicating with said second injector slots.
 5. The diffuser apparatus as defined in claim 4 in which said collector means further includes an inner structural ring connected to said central hub and to said first combination plenum and structural support member.
 6. The diffuser apparatus as defined in claim 4 which said collector means further includes an outer structural ring connected to said central hub and to said second combination plenum and structural support member.
 7. The diffuser apparatus as defined in claim 6 further including: (a) a first reinforcement plate or built-up structure connected to said first combination conduit and structural support member; and (b) a ground plate or built-up structure connected to said first reinforcement plate or build-up structure.
 8. The diffuser apparatus as defined in claim 7, further including a second reinforcement plate connected to said second combination conduit and structural support member.
 9. A diffuser apparatus for use in connection with a gas turbine of the character having a rotatable power shaft and a plurality of rotating turbine blades, a high velocity gas stream exiting the turbine blades, said apparatus comprising: (a) a central hub for supporting said rotatable power shaft of said turbine; (b) a shroud circumscribing said hub, said shroud having inner and outer walls defining an enclosure having a first open end disposed proximate the turbine blades to receive the high velocity gas stream, and a second discharge end for exhausting gases of said high velocity gas stream, said inner wall of said shroud having first injector slots provided therein and said outer wall of said shroud having second injector slots provided therein; (c) capture means disposed proximate said second discharge end of said enclosure for capturing a portion of the gases of said high velocity gas stream, said capture means comprising a generally toroidal-shaped capture scoop; (d) collector means circumscribing said discharge end of said shroud for collecting gases flowing therefrom, said generally toroidal-shaped scoop being disposed interiorly of said collector means; (e) first combination conduit and structural support member for providing rigidity to the diffuser, for maintaining concentricity between said hub and said shroud during operation and for directing a portion of the high velocity gas stream captured by said capture means toward said first injector slots provided in said inner wall of said shroud; and (f) a second combination conduit and structural support member for providing rigidity to the diffuser, for maintaining concentricity between said hub and said shroud during operation and for directing a portion of the high velocity gas stream captured by said capture means toward said second injector slots provided in said outer wall of said shroud.
 10. The diffuser apparatus as defined in claim 9 in which said collector means further includes: (a) a first combination plenum and structural support member circumscribing at least a portion of said inner wall of said shroud for providing rigidity to the diffuser and for maintaining concentricity between said hub and said shroud during operation, said first combination plenum and structural support member having a gas inlet and a gas outlet communicating with said first injector slots; and (b) a second combination plenum and structural support member circumscribing at least a portion of said outer wall of said shroud for providing rigidity to the diffuser and for maintaining concentricity between said hub and said shroud during operation, said second combination plenum and structural support member having a gas inlet and a gas outlet communicating with said second injector slots.
 11. A diffuser apparatus as defined in claim 9 in which said collector means further includes an inner structural ring connected to said central hub and to said first combination plenum and structural support member.
 12. A diffuser apparatus as defined in claim 9 in which said collector means further includes an outer structural ring connected to said central hub and to said second combination plenum and structural support member.
 13. A diffuser apparatus for use in connection with a gas turbine of the character having a rotatable power shaft and a plurality of rotating turbine blades, a high velocity gas stream exiting the turbine blades, said apparatus comprising: (a) a central hub for rotatably supporting the power shaft of the turbine; (b) a shroud circumscribing said hub, said shroud having inner and outer walls defining an enclosure having a first open end disposed proximate the turbine blades to receive the high velocity gas stream, and a second discharge end for exhausting gases of said high velocity gas stream, said inner wall of said shroud having first injector slots provided therein and said outer wall of said shroud having second injector slots provided therein; (c) capture means disposed proximate said second discharge end of said enclosure for capturing a portion of the gases of said high velocity gas stream, said capture means comprising a generally toroidal-shaped capture scoop; (d) collector means circumscribing said discharge end of said shroud for collecting gases flowing therefrom, said generally toroidal-shaped scoop being disposed interiorly of said collector means, said collector means further comprising: (i) a first combination plenum and structural support member circumscribing at least a portion of said inner wall of said shroud for providing rigidity to the diffuser and for maintaining concentricity between said hub and said shroud during operation, said first combination plenum and structural support member having a gas inlet and a gas outlet communicating with said first injector slots; and (ii) a second combination plenum and structural support member circumscribing at least a portion of said outer wall of said shroud for providing rigidity to the diffuser and for maintaining concentricity between said hub and said shroud during operation, said second combination plenum and structural support member having a gas inlet and a gas outlet communicating with said second injector slots; and (e) first combination conduit and structural support member for providing rigidity to the diffuser, for maintaining concentricity between said hub and said shroud during operation and for directing a portion of the high velocity gas stream captured by said capture means toward said first injector slots provided in said inner wall of said shroud; and (f) a second combination conduit and structural support member for providing rigidity to the diffuser, for maintaining concentricity between said hub and said shroud during operation and for directing a portion of the high velocity gas stream captured by said capture means toward said second injector slots provided in said outer wall of said shroud.
 14. A diffuser apparatus as defined in claim 13 in which said collector means further includes an inner structural ring connected to said central hub and to said first combination plenum and structural support member.
 15. A diffuser apparatus as defined in claim 14 which said collector means further includes an outer structural ring connected to said central hub and to said second combination plenum and structural support member.
 16. The diffuser apparatus as defined in claim 15 further including a reinforcing structure connected to said first combination conduit.
 17. The diffuser apparatus as defined in claim 16 in which said reinforcing structure comprises: (a) a first generally vertically extending reinforcement plate or built-up structure connected to said first combination conduit and structural support member; and (b) a ground-engaging plate or build-up structure connected to said first reinforcement structure and operably associated with said first generally vertically extending reinforcement structure.
 18. The diffuser apparatus as defined in claim 17 in which said reinforcing structure further includes a second reinforcement plate or built-up structure connected to said second combination conduit and structural support member.
 19. The diffuser apparatus as defined in claim 18 in which the diffuser has a vertical plane of symmetry and in which said first reinforcement plate or built-up structure is located in the vertical plane of symmetry of the diffuser.
 20. The diffuser apparatus as defined in claim 19 in which said first and second reinforcement plates or built-up structures are located symmetrically around said first and second conduits. 